Double heterodyne radio receiver



Aug 5. 1952 R. BATAILLE ETAL DOUBLE HETERODYNE RADIO RECEIVER "7 Sheets-Sheet 1 Filed 001'.. 18, 1946 Aug. 5, 1952 R. BATAILLE ETAL DOUBLE HETERODYNE RADIO RECEIVER '7 Sheets-Sheet 3 Filed Oct. 18, 1946 f. ,mmf/M@ e/ @i2 fs ,ff a@ DM@ Aug. 5, 1952 R. BATAILLE VErm. 2,606,285. DOUBLE HETERODYNE RADIO RECEIVER EMME@ War-my:

Aug. 5, 1952 A R. BATAILLE Erm. 2,606,285

DOUBLE 4EETERODYNE RADIO RECEIVER Filed OOt. 18, 1946 7 Sheets-Sheei'l 5 5' MEMME daarheys Aug. 5, 1952 v R. -BATAILLE ETAL I 2,606,285

DOUBLE HETERODYNE RADIO RECEIVER Filed oct. 18, 1946 'r sheets-sheet e J-sclLLATlNs clRcurr osclLLATme clRculT GENERATOR HARMONICS R. BATAILLE 'ET AL DOUBLE HETERODYNE RADIO RECEIVER Aug. 5, 1952 Filed Oct. 18, 1946 f mm k .H my

Patented Aug. 5, 1952 i2-rice BOXUBLE BETER-SEYNE lRADI() RE CEIVER.

Roger Bataille and Georges Honorat,-Neuillysur Seine, France, assignors to Societe Franaise des Telecommunications, Neuilly-sur-Seine, France, a corporation of France y Application October 18, 194,6, SerialjNogMg'fi In France November 23, 1942 f 'section 1, Public Law 69o, Augustl 8,-119'46 i Patent expires Nveniber`23, 1962 soiaims. (Umso-2o) It has longrbeen a problem'for those skilled in the art to stabilize radio-electric transmitters" as Well as receivers inorderthat they vmaybe tuned on-a previously determinedconstant Wave length for any desired position of their controls. In the devices oi the conventional type, the desiredfrequency variations in transmission as well as in reception are obtained by means of fat least one 'variable'capacitoi-.- Under the effect of a number of factors, such as variations in temperature, pressure, etc.,rtl1e resonant frequencyY may vary in the conventional devices for the samefposition of the controlling member by about V1000; vfor frequencies higher than -50 kc., this variation may escape the tuned band of 'a receiver which is initially correctlyadjusted. This is the'i'eason Why it has Abeen necessary until now to tune up the receiver, i. e. to use` a trial and error method, appreciating acoustically the changes in intensity of-the 'reception and even, in certain cases, to alter the adjustment ofthe receiver during prolonged'reception.y

nttempts'have already beenmade to eliminate of defects, Vparticularly in the militaryeld-where the necessity of transmitting over `one or vmore previously determined `irequencies of la limited numberpermits easy -identification of the user. iof theseirequencies.

`The present invention has for 'its object to benet simultaneously "from 'the advantages inherent to oscillating devices v'of tl'ie quartz i type andA to oscillators of theic'ontinuous'btype, forexample V a va'riable capacitor;` With'v the addedbenefit vof eliminating simultaneously the defectsof these devices. yAccording vtothe invention, the frequencyband on which it is `desired to 'operate continuously and vwhich may be `a very large one-even a. band covering all 'the vfrequencies used :in radio `transmission-is covered by one or more I quartz devices, preferably not more than one or two, Which,"takingf into account the'harmonies 'of the crystal or crystals, evenly divides the ove'rallband into --a plurality of elementary bands `which may be Vcovered continuously by means of van :oscillator of known continuously variableftype. Zin-other Wcrdsif it is desired to tunera'receiveraccording .to the invention to any Wave 'length'vvhich the set/may use', the set is tunedfb'y means'of a quartz device on an-approximate frequency supplied by fthe piezo-electric os,- cillations, and the :negative or positive V complement to .obtain the .desired AWave length is sup,- plied `.by 'the continuously variable I, oscillator.

It is readily seen,ontli e. one hand,- that the whole of the bandinay be covered in a continuous manner as in thecase of an oscillator of the conventional type andon'the other hand, that the maximum error introduced, which is obviously the sum ofthe errors introduced by the quartz '.deviceand by the continuously variable oscillator, vis always very small. Theerror resulting fromthe quartz device, amounting to only .1/1'00000 of `the frequency, always remains verygsmall even if this frequency is'high; the error introduced'by the continuously variable oscillator, :though amounting to 1/1000 of its frequency, is small, since this frequency has such a `small .absolute value, amounting only to the requisite complement to be addedto the frequency of 'the' quartz device. f

:If it 'is Adesired for example to continuously covera'band from() (theoretical) to.30,000 kc. or, more probably, fromvlOO kc. to 30,000 kc. the following. method may be used:

A iirst `quartz, stabilized oscillator provides crystal frequencies of 1000, 2000 etc. up to 30,000 kc. which differ one from the other by 1000'kc. Asecond oscillator, againquartz stabilized, provides in each of the 100G-kc. sections. thus vdefined, intermediate 'divisions `having a 100, 200, 300 etczfup to a 1000. kc. difference. A third'continuously variable conventional oscillator having a range of from to 200 kc. provides a continuous variation in each of the 100 kc.I bands thus limited.

The maximumerrors thus introduced are as follows; in thelrst quartz circuit, 0.30 kc.;in the second quartz circuit 0.01 kc.; inthe continuously variable circuit'OLZ RCL; i. e. a total of 0 0.51 kc. This maximumvariation will not exceedtlfe "normallband pass range of a receiver so that the latter keeps tuned in spite of any disturbing factors vWhich may occur. lAccordingly, to obtain stable reception on any desired wavellengtnitwill only be necessaryvto adjust the controls ofthe vreceiver tothe position corresponding-to said wave length, Awithout groping or continuousiaudiblemonitoring.

On theiotherlhandthe resulting! frequency has no troublesome parasitic frequencies, the nearest one being -30 decibels, far from any useful final reception, even in the most unfavorable case.

In the above example, the control operations for reception are limited to three:

(l) Selection of the l000ths by means of a 30l band to secure continuity between the frequen- Y cies of the oscillations obtained by piezo-electric means.

Said receiver has only a small drift and may be tuned on a determined frequency by bringing its controls opposite the figures corresponding to frequency divisions, the stability of the control being good enough to maintain the tuning in spite of any disturbing factor.

The receiver thus allows the reception of transmissions of any frequency within a band of any desired width defined by the local oscillator or oscillators and their harmonics.

In this form of receiver the received oscillations are subjected in a standard mixer stage to a first frequency change by means of a local oscillator, the frequency of which is piezoelectrically stabilized, the resulting oscillations having an intermediate frequency restricted to a relatively narrow frequency band. 'I'he second local oscillator with the continuous frequency variation thus may have an inherent frequency low enough to introduce only a small frequency drift, the division of the incident frequencies into sections due to the effect of the frequencies of the first local oscillator being such that inno case will the latter cause troublesome interference to reception.

In the preferred embodiment of the invention the injection of this first local Yfrequency having an amplitude necessarily higher than that of the incident oscillations may be made without disturbing effect on reception due to the fact that its effect on the stages following the mixer is eliminated by means of an opposition arrangement.

The various piezo-electric stabilized local frequencies may be obtained by means of a small number of crystals due to the fact that the oscillator or oscillators controlled by the latter include a harmonics generating and 'selecting device.

In the following description, reference is made to the annexed drawings in which:

Fig. 1 is a general block diagram of a radioreceiver according to the invention;

Fig. 2 is a block diagram of a receiver according to the invention;

Fig. 3 shows the controls of the receiver shown in Fig. 2;

Fig. 4 is a circuit diagram of the receiver shown in Fig. 2; Y

Fig. 5 is a block diagram of a receiver according to an alternative embodiment;

Fig. 6 is a pictorial representation of the local oscillation and intermediate frequencies resulting from an embodiment of the receiver;

Fig. '1 is a schematic diagram of a local oscillator used in the receiver;

Fig. 8 is a diagram similar to Fig. 7 `showing an alternative embodiment;

Fig. 9 is a circuit diagram of a receiver employing the oscillation generator shown in Fig. 8.

' It is pointed out that in the following description the figures given for the frequency values are intended only for a proper understanding of thedescription. As such, they are only illusvtrative numerical examples.

Referring to Fig. 1, A is an oscillator of the conventional continuously variable frequency type, for example a heterodyne. B is a piezoelectric crystal oscillator capable of adjustment to a number of determined frequencies, namely the basic frequency of the crystal and a number of its harmonics. C is also a piezo-electric crystal oscillator capable of adjustment to a number of determined frequencies, namely the basic frequency of the crystal and a number of its harmonics.

If, for example, it is desired to cover with this device a continuous frequency band between 100 kc. and 30,000 kc., the oscillators may be selected with characteristics such that the oscillator A will generate oscillations capable of continuous variation from 100 kc. to 200 kc., the oscillator B will generate frequencies of 100,200, 300, etc. up to 1000 kc., and the oscillator C will generate oscillations of a frequency of 1000, 2000, 3000, etc. .up to 30,000 kc. If, for example, it is desired to tune the set on the 25,495 kc. frequency, the oscillator C will be adjusted on 25,000 kc., the oscillator B on 400 kc. and the oscillator A on 95 kc.; said frequencies are added and the final frequency is the desired frequency. This frequency is obtained with a maximum errorof 0.5 kc. as stated above.

Figure 2 is a block diagram of a receiver according Vto a preferred form of the invention. It must be understood that the various figures stated for said receiver do not have an absolute value and are given only for the purpose of better understanding of the construction and operation.

The receiver comprises a pre-selection filter 25, receiving from an aerial 25a transmitted radio frequency oscillations which may theoretically vary from 1 to 24,000 kc. Said oscillations having a frequency designated F1 are led to a first frequency changer stage 26 simultaneously with the local oscillations from a piezo-electric generator 21, controlled according to the operation of the pre-selection filter 25. The frequency F2 of the-oscillations from the generator 21 may vary by 1000 kc. steps from 0 (theoretical) to 23,000 kc., The piezo-electric crystal of the generator 21 has, for example, a basic reasonant frequency of 1000 kc. and from this basic frequency supplies the various harmonics up to 23,000 kc.

The frequency changer stage 26 is so designed as to produce oscillations of a frequency l"3 equal to thesum or difference of frequencies F1 andl F2. A filter 28 receiving the oscillations of frequencies F1, F2, and F3, eliminates both of the e first frequencies, passing only the frequency F3,

continuously variable frequency generator y52 'ef conventional for-m. r

The ypiezo-electric crystal controlling the generator sillas, for example, a basic frequency of 1000 kc. Aand 4supplies the various harmonics necessary to Vhave a frequency varying -by 100 kc. steps :between-400 and 1300 kc. The frequency F5 vmay vary in a continuous mannerover a 100 kc. band, for example between 125 and 225'kc. l f 1 vThe oscillations of frequency Ffand Athose -of frequencyF are led to a-n'lixing device 33, aggregating them to frequency FG; Filter T30-re- 'ceiving the` oscillations of frequency F4, F5 and F6,*Will' pass only the frequency F6 vwhich may thus vary in a continuous manner from 525 to 1525 kc. f

' Theoscillations of F3 frequency and'those o'fif frequency, lthe former varying from 1000 to l:2000 kc. `and they lattervarying from `525 to v1`525Vkc., aref'led to the second frequency changing stage 23 having their difference at a constant value equal to 4'15 kc. which constitutes the final intermediate frequency of the receiver.

' '-Ifheremaining part of the set -is of standard design. It may include, for example, an intermediate frequency device 34 vwhose oscillations are led simultaneously with the oscillations of a local generator 35, at a constant frequency of 474 kc., to a detection device 36. The audio frequency signal, suitably amplified by a device 31, will be led to a loudspeaker 38. v

Referring now to Fig. 3 showing certain features of the construction and operation of the receiver according to the invention, more specifically its controls, the set includes vthree control knobs: a knob 39 for the selection of the kc.Y thousands, a knob 40 forthe selection of the kc. hundreds and a knob 4I for the kc. units between 0 and 100. f n lKnob 39 controls a handlever 42 of the'preselection lter 25 and a handlever 43 of the generator 21. The knob 39 moves on a scale graduated 'from 0 to 23 and has twenty-four steps. The twenty-four corresponding positions -of handlever 43 of the generator 21 enables the 'latter to be tuned to the frequencies 0 (theoretical), 1000, 2000, 3000, etc. 23,000 kc.

= Knob 40 has ten steps and controls ahandf lever '44 of the pre-selection filter 25, a .handlever 45 of the filter 28, a handlever 46 of the filter 30 and a handlever 41 of the generator 3|. Adjusting the pre-selection filter 25 by means of handlevers 42 and 44 will roughly tune'up the latter on a 100 kc. range to the radio frequency of the incident oscillations to be received.

. Knob 4l, which may be moved in a continuous manner, controls a variable capacitor 48 or the like 'to tune filter 28, a variable capacitor 49 or the like to tune lter30 and a variable capacitor 50 or the like to tune the continuously variable generator 32.

Filter 28 may thus, by operating the Ahandlever 45 and the variable capacitor 4.8, be adjusted continuously on the intermediate frequency F3 comprised between 1000 and 2000 kc. The frequency changer 26 is fed by filter 25 and bygenerator 21 in such a manner that, in the most unfavorable case, the image will be at 2 F3, i. e. at a of 2000 kc. from the frequency kto be allowed to pass and accordingly the .attenuation of the image to 60 decibels may be secured by the `conventional means, the tuning `.up being made for any point of the 100 kc.

6 passing band, at f-a `maximum `of 3l decibels v.fro the point -of the centered frequency. Y

Filter 30 is adjusted through the `'operation of handlever 45 and variable :capacitorv49 'to the suitable frequency between 525 and 15251-kc.fthis adjustment being made by the handlever y'46pm' kc. steps and by the variable capacitor 49 within said steps.

The frequency F6 of 'the oscillations issuing from filter 30 varies and is synchronized with the frequencies generated on the one `hand by generator 3l and on the other `hand by generator 32; the handlever 41-of-the-generatcr 3|, aswell as -the handlever 46, being fdriven by knob '411,` and the varia.ble'--capacitor Y50V of generator 32, as well as the variable capacitor v'45). being 'driven byknob 4|. I 'l In 0 position o-f knob 39, the frequency jlF2 generated by the generator 21, amounts. to '1000 kc. and is added to incident frequency F1 in such a manner that thei-ncident frequencies F1 com# prised between `0 (theoretical) and v1000 kc.,'fw`ill due to the frequencychange inthe device 21:,be transformed into oscillations `of -a frequency comprised between 1000 and -2000^kc. l

In position 1 of knob 39, generator `21"is"d'i'sconnected. The frequency changer'ZS operates then as a direct amplier and transfers without frequency change to filter 28 fthe incident-frequency comprisedbetween 1000 and 2000`kc.-9

In position 2Aof knob 39, 'the frequency of lthe generator 21 will be again 1000 kc. andwill be subtracted from the incident frequency comprised between 2000 Aand 3000 kc. l

The intermediate frequency yF3 will befthus again comprised between 1000 and 2000 kc., the same applying to every vhigherl position, 3, 14,- '5; etc. 23.*of'knob 39.v V

It is obvious that various combinations ofjsub-l traction oradditicn of vfrequencies may berused, changing, if necessary, the Valuel of the 'free quencies .from-:generator 2-1 `by correspondingly changing the positionof handlever 43.

The receiver according to the invention allows, insertingif necessary a double frequency changer, covering the whole chosen reception band in a continuous manner, for example from 0 (theoretical) to 24,000 kc., without changing the Ainl termediate frequency. Accordingly, a -control usually :found in receivers of known type is eliminated, vproducing an importantand practical simplification. Y

In addition, the .operation of the unit fsc'ale from end to end always corresponds :to a 100 kc. band for any considered range o-f frequency; `thus a uniformspreading of .the wave lengths will beobtained for any desired frequency.

The receiver according to the finventionvlhas perfect stability, high enough ,to tune up :at will to the desired transmission by simply adjusting the graduated dials to the figure characterizing the frequency of the transmitter, without the necessity ofV using a trial and error method as in the case of receivers of known type. Y

In the most unfavorable case, i. e. in `there-- ception of a transmission on 24,000 kc., thezmaximum possible drift will be the sum of the following drifts:A

(a) The drift correspondingto oscillationsf'of Aa 23,000 kc.,frequency vof the oscillator ,device 21, which, being of piezo-'electric type, has a precision of 1,400,000; the maximum driftof vsaid oscillator 21 will accordingly be 0.23 kc.

(b) The drift .introduced by the oscillator .3|. of piezo-electric type, reaching a maximum when the oscillations generated have a value of 1300 kc., and amountingto 1A00,000 of said value, i. e. to 0.013 kc.

(c) The drift introduced by the continuously variable generator 32 which for the maximum of 225 kc. amounts of i000 of said value. i eto 0.225 kc.

The maximum total drift for the receiver will thus be 0.468 kc., i. e. a figure small enough to remain withinthe limits of receiver drift and interference. A more detailed-diagram of the receiver will now be described with reference to Fig. 4. The incident oscillations caught by the aerial a are led to the pre-selection device comprisingr two oscillating circuits, parallel connected, the first one comprising multi-tap inductance s1 and capacitor c1; the second oscillating circuit comprises a multiftap inductance s2 cooperating with the handlever :44; The first oscillating circuit may be tuned up, according to the handlever position 42on frequencies of 0,1000, 2000, etc. 23,000 kc., and the second oscillating circuit may be tuned up onten successive frequencies having an intervalof 100 kc. between them. 4The pre-selection lter vmay thus be tuned upon 240 successive bands, each having a width of 100 kc. ,1 f

The oscillations of a frequency F1, from the preselection filter, are fed to a mixer tubell, in which r1 is the control grid leak resistor (automatic volume control) and c3 is the uncoupling capacitor of said grid. r6 is the screen-grid resistance of tube l1 and e8 is the uncoupling capacitor of said screen-grid. The injection grid of tube l1 is connected to an oscillating circuit comprising a multi-tap inductance s3, and capacitor c2 corresponding to the various taps, in orderA to tune up said oscillating circuit, in the selected example to 0, 1000, 2000, etc. 23,000 kc. c4 is the coupling capacitor of the injection grid of tube l1 and r2 is thegrid leak resistor. The oscillating circuit s3-c2 is insertedat the outlet of a harmonic generating tube Z2, of -Which T5. is the screen-grid resistance, and T7 theY uncoupling capacitor of said grid. Tube Z2 is inserted after an oscillating tube Z3, fed by a piezo-electric crystal q1, having a basic frequency of 1000 kc. for example. r4 is the grid leak resistor of tube Z3. The oscillating circuit, in which tube l3 is inserted, comprises an inductance s4 and a capacitor c6 and is tuned up to a 1000 kc. frequency. The connection between tube I3 and tube l2 comprises a capacitor c; r3 is the grid leak resistor oftubelz.

At the outlet `of tube'l1 is an oscillating circuit consisting in a multi-tap inductance S5, controlled'by the handlever 45, and a variable capacitor cvl, the capacity of which may vary continuously over a 100 kc. band. Padding capacitors are series connected `to the taps of winding S5 for ganging purposes. The oscillations from tube l1 are fed to a tube Z4 through a coupling capacitor c9 andl vthus may vary continuously from 1000 to 2000 kc., per 1000 kc. step.

-Tube Z, Ywhich is the second frequency changer, is for example of the triode-hexode type. r" is the control grid leak resistor 'forautomatic de-polarization and constitutes an 'automatic volume control; clgis the uncoupling capacitor of said grid. The feeding resistor of the screen grid is shown at 116 and the uncoupling capacitor at 019. The injection grid of tube l4 is fed through an oscillating circuit comprising a multi-tap inductance s6 and a variable capacitor co2 in order to be continuously tuned up from 525 to 1525 kc. The inductance s8 allows tuning to 525. 625 etc. 1425 kc. and the capacitor co2 permits covering of the kc. band over each of the above values. Padding capacitors are series connected to the taps of inductance s6 for ganging purposes. Said oscillating circuit and tube l* are connected by a capacitor `01; 1's is the injection grid leak resistor of said tube.

The oscillating circuit comprising the inductance s and the capacitor cv2 is inserted at the outlet of an oscillating mixer tube 15, of the triode-hexode type for example. The latter tube generates oscillations, controlled by the oscillating circuit formed by inductance s" and variable capacitor e123; r1 is the feed resistance of the oscillating plate and cl2 is the uncoupling capacitor of said plate; c11 is the coupling capacitor of the oscillating grid. Said oscillations are mixed with those received by tube l5 from tube l'. through a coupling capacitor c1a T15 is the injection grid leak resistor of tube l5; r11 is a feed resistance of the screen-grid of the hexode and c1 is the uncoupling capacitor of said grid. The harmonics generating tube l is fed by the oscillations from a tube l" for example of the triode type, and controlled by a piezo-electric crystal c, whose basic frequency amounts for example to 100 kc. The circuit of tube 17 comprises the inductance and the capacitor c and is tuned up to 100 kc. r1* is the oscillating grid leak resistor. v

Coupling between tube lI and tube I's is performed through capacitor C17; r is the grid leak resistor of tube Z; r1 is the drop resistance of the screen grid of said tube ando15 is the uncoupling capacitor of said grid. At the outlet of the plate of tube l6 is an oscillating circuit comprising a multi-'tap inductance sa, having ten taps in the example shown, the handlever 41 of which also connects into the circuit corresponding capacitors c, for tuning up to 400, 500, etc. 1300 kc. The outlet of the plate of tube l4 is connected to the intermediate frequency of the receiver, said device as well as those following it in the receiver being of the conventional type.

The control knob of the thousands mechanically drives the handlevers 42 and 43; the knob of hundreds drives the handlevers 44, 45, 46; the knob of the units drives the variable capacitors co1 (48), co2 (49) and cv? (50).

A detailed description of the manner of operation of a further embodiment of a receiver constructed in accordance with the invention is as follows, illustrative numerical values being used.

Referring to Figure 5 showing a block diagram of the receiver, the incident oscillations having a frequency F20 are caught by the aerial |50 and are led to a high frequency amplifier |5|. Here they are submitted to a first change in frequency in a device |52, the structure of which will be described hereafter, and which is also fed by oscillations of a frequency F21 generated by a local oscillator |53.

The resulting oscillations, of intermediate frequency F22, are led to a second frequency changer |54, which is also fed by oscillations of a second local oscillator |55; the resulting oscillations from frequency changer |54 will be the intermediate frequency oscillations of the receiver having a value F24.

The oscillations from the frequency changer |52 always have, due to the oscillations generated by the first local oscillator |53, a frequency of a relatively low value for any frequency of the in- 9. cident. oscillations, and accordingly .the oscill'aetions of the second localoscillator |55, also may always. have a relativelyflow-V value in. order' to obtain. the nal intermediate: oscillationsfof. fixed frequency. The rstz'cscill'ator' |53, controlled piezo-electrically;introduces' only ay very small drift; The second localoscillator, generating'oscillations with a frequency of a relatively low value, may'beof. the conventional continuously VaryingA type, and introduces an acceptably. small drift. f

If for example it isdesired` to keep the value of the frequency F22'between 2 and4 megacycles in order-to use' ay local' oscillator whose frequency F22 may vary between 1625 and 3525 lia-inthe case of a final' intermediate frequency equal to 475 kc., it will be necessary, in order to receive incident oscillations comprisedl'between 2` and 2O megacycles, to generateflocal oscillations of' F21 frequency equal to- 0,2, 4; 6 etc: 14, 16 megacycles;

This is shown i'n the diagram of Fig: 6 in which thevalues of the frequency F2"of the incident oscillations are'in abscissas and the intermediate frequencies F22 in ordinates. Thus aseries of parallel diagonal straight lines are obtained, the value of the local frequency F21 to' besupplied being'constant for anyone of' said lines. Said Value is shown in the diagram adjacent' to the corresponding diagonal. line.

In the considered example, .a first solution con.- sists in using a local oscillator L53 controlled by a piezo-electric. crystalhaving a. frequency =equal to 2 megacycles. andA inthen. yextractingsuccessively the various liamnonics.Y But` then it would be impossible to.. receiveQincident'oScillations of a frequencyequal to2 megacycles and to all the multiples of 2 megacycles, because for said values, the local oscillations would always contain the basic frequency equall to 2' mega'- cycles which would cause troublesome interference.

In such case, the present invention further consists in generating local oscillations whose basic'frequency may be, at will, 2, 4, 6, or 8 megacycles, obtained for example by means ofv an oscillator which may be controlled atwill by one of four piezo-electric crystals, having resonant frequencies respectively equal to 2, 4, 6, 8 megacycles.

The local frequency of 2 megacycles will be used to receive incident oscillations comprised between 4 and 6 megacycles. The latter frequencies may not be received, of course, in this band due to the interferences caused bythe local oscillations having a basic frequencyA of 2 megacycles. However, the incident oscillations of a frequency equal to 4 megacycles may be received by short-circuiting the local oscillator |53.

As regards the incident oscillations of a, frequency comprised between 6 and 8 megacycles, the frequency F21 will equal 4 megacycles. This local frequency does not cause any interference except with incident oscillations of a frequency equal to 8 megacycles, but not for those oscillations having a frequency of 6 megacycles.

It is understood that the incident oscillations of 6 megacycles frequency, which could not be received when using a local frequency of 2 megacycles, will be received with a local frequency equal to 4 inegacycles.

In the diagram a small black circle has been placed at the ends of the diagonal lines corresponding to incident frequencies which can not be received when using the local 'frequency cor'- 104 responding to. said. line; they are marked. with a whitecircleintheotherLcase., n

Thev ends." of the next.Y diagonal. line. are both marked with-.aiwhite circle', 8 and 10. not being multiples of" 6T, as well as those ofthe next` succeeding line, 10i and 12. notzbeing multiplesof'.

'I o receive incident oscillations'. ofi higher' frequency, the local oscillations which areI `used consist in the harmonics of those used. to receive oscillations oft frequencies between 2 andv 12 megacycles.`

For the' reception of oscillations between l2 and 1'4 megacycles, a frequency F21' is selected equal to 10 megacycles. It will be obtained by using thel 5th harmonic@ of the oscillations supplied by the crystal having a basic frequency of 2V`megacycle's. Said basic-frequency prevents the reception ofthe band endsvwhenusing'saidv local frequency, 12 and 14l being multiples of' 2.

To' receive incident" oscillations between 14' and 16 megacycles, the-F21-frequencyfismade' equalto: 1'2 megacycles. It will be obtained: by'usingf the 2nd harmonic of the local oscillations having a basic frequency of 6`v rnegacycl'esl The reception of' end frequencies is` then possible, neither 14nor 16 being'multi'ples' of 6T.

The frequency F21 for' thereception of o'scil lations between 16 and 18- megacycl'es is made equal to 14 megacyclesand' is obtained with the 7th harmonicv of" the oscillations of the2 megacycles crystal. The'end frequencies of the band then can not'bel received, 16 andv 18` being' multiples of 2.

vTo receive incident oscillations of afrequency between 18v and 2'0 megacycles; the frequency F21" is' made equal toi'- 16VA megacycles' andv is obtained" `by the 2nd harmonic of the local oscillations of basic frequency equal to 8 megacycles. The ends of the band are then received, neither 18 nor 20 being multiples of 8, etc.

In the selected example, when using only four basic local frequencies, incident oscillations of any frequency may be received, comprised in a band as wide as desired, including oscillations having a frequency which is a multiple of the band width of the intermediate frequencies F22.

This property is shown in the diagram of Fig. 6v by the fact that there are never two black circles on the same vertical line.

In practice, when the end of a band can not be received, the end of the adjacent band may be slightly extended. For example, the local frequency of 4 megacycles allows reception of incident frequencies having a value slightly lower than 6` megacycles.

The following table gives, in megacycles, the various values of frequencies considered for the reception of incident oscillations, the frequency of which is comprised. between-2 and 20 megacycles.

An alternative emb'odimentof'the presentv inivention allows theluse'of only'two'piezo-electric crystals adjustedtotheihighest' basic Vfrequencies in the examplek previously'considered', .namely,1 6

and 8 megacycles, inorder'to obtain lo'caloscil'- lations for the first frequency vchanger'.

' According to Athis alternative, the oscillator 'device corresponding to one of' the crystals feeds a first frequency changer. device whose resulting oscillations are used in the'feed of a secondfrequency changer. r i

Fig. 1 shows a schematic of such an arrangement. An oscillator |56 feeds afirst injection 12 adjstingto said value, tube |56 operating then asa :harmonics generator).

Accordingly, withtwo crystals respectively adjusted to. 6`and 8 megacycles, oscillations may be obtained at will having a frequency equal to 2, 4, 6-8 megacycles, free from sub-harmonics, and 10, V12, 14, l'megacycles, allowing thus. the reception of incident oscillations of any frequency comprised between 2 and 20 megacycles.

grid |51 0f a frequency Changing tubef'l58. 10 According to the invention, both arrangements 'Ihe plate circuit |59 of said tube is tunedup may be combined to obtain said local frequencies, by an oscillating circuit i60 and is connected to a. in a single arrangement shown schematically in harmonic generating tube |6|, whose plate circuit Fig. 8.A The'oscillating device |56 comprises two is tuned up by an oscillating circuit |62 conparts |56".and |56 stabilized by crystals respecnected to a second injection grid |63` of tube 15 tively adjustedto 6 andmegacycles. The oscil- |56. 1 y Y lating circuit |60 may at will be adjusted to 2, 4, The Oscillating circuits |60 and |62 are such 12'and 14 megacycles. The oscillating circuit |62 that the frequency corresponding to circuitV |60 is permanently adjusted to a value of 4 megaequals the sum or the difference of the frecycles. An oscillating circuit |64 is series conqueneies correspondingtooscillator |56 and to 2O nected into the anode circuit. of tube |6| and oscillating circuit |62. Under such conditions, may be adjusted to 10 and 14 megacycles. once tuned up, the tube |58 will operate as a With this single arrangement, the local frefrequency changer. v quencies may be drawn from connections |66,

If for example, the oscillator |56 be stabilized |66, |61 and |68 with the controls stated as reby a piezo-electric crystal of a resonant frequency 25 gards the oscillating circuits |60 and |64. equal t0 6 megacycies and if the Oscillating cir- The following table gives the various resulting cuits |60 and |62 be adjusted IeSpeCiiVeiyiO 2 frequency values for the above discussed numeriand 4 megacycles, saidarrangement-may supply @a1 examples; oscillations of a frequency equalto 2 megacyc es 4(taken from'oscillating circuit |60); oscillations ..0 F2=mc1denta1 frequency of a frequency equal to 4 megacycles (taken from l F2 :mst lfcaiffequency oscillating circuit |62), oscillations of a frequency F22=1`Su1t1ng Intermediary frequency equal to 6 megacycles (directly drawn from'the F2=requency from 0501119501' |56 osciuator |50), osoiuauons of a frequen'ey'equai F2G=frequen =y Ofvoscillating circul' |60 to l0 megacyoles (from the 5th harmonic .ofthe ,5 F27=frequency of oscillating circuit |62 oscillations from tube 16|), oscillations of afre- F28=frequency of oscillating circuit |64 F20 Fu F20 F21 Fu Fn Fn .10. 000 s. 000 0 0 0 s. 000 2. 000 12.000 8.000 0 0 l 0 8.000 4.000

1s. 000 s. 000 10. 000 0 0 10. 000 2. 000 20. 000 s. 000 10. 000 0 0 10. 000 4. 000

quency equal to 12 megacycles (drawn from 7os- Fig. 9 is a detailed schematic diagramof a precillating circuit |60 adjusted then to said value, 60 ferred form of a receiver according to the inthe tube |58 operating then as harmonics gen- Vention. The incident oscillations caught by the erator), oscillations of a frequency equal to 14 antenna |50 flow in an antenna circuit |10 commegacycles (drawn fromtube |6| of the '1th harprising two adjustable contact members |1| and monic of the oscillations feeding said tube). |12, the various steps of which correspond to If in the arrangement shown in Figure '1 the 05 inductance taps and a controlled variablecapacioscillating circuit |60 be adjusted to avalue equal tor |13. Said oscillations are amplified in a to 4 megacycles, the oscillating circuit |62 retube |14, the plate-circuit |15 of which also maining the same as previously, and if the oscilcomprises two controlling contact members |16 lator |56 be stabilized by a piezo-electric crystal and |11, having steps corresponding to induchaving a proper frequency of 8 megacycles, it is 70 tance taps, and a variable capacitor |18. The obvious that said arrangement may supply oscilcontactors |1|, |12, |16 and |11 are coupled by lations of a frequencyV equal to 8 megacycles a linkage |19. They are, for example, fitted on (drawn directly from the oscillator |56) and and keyed to the same shaft. oscillations of a frequency equalto 16 megacycles The oscillations from plate circuit |15 feed a (drawn from the oscillating circuit |60, then 75 grid |80 of a frequency changing tube |6|. Said tubesis also fedi oniboth'itszother grids |821 and. |831by.- theflocal oscillations from alocal': oscil.n lator. |53-, Which.` mayibe; as previouslydescribedv in.thereferenceitoulligure 8... Said oscillatonicom-f prises :two piezo-electric: crystals; |184? and; 85X adjusted respectively: as: the aboveA describedfexample,v tor 6fand18 mega-cycles and controlling; an oscillator-tube |811. Eiga shows thewarousgparts of fthe:Y unitv representedinlig. 9.1

The contactingrmembersi |88.; |39; i361 and .ilflf to: select: the frequencyY of f locali oscillation; are connected together: by. a; linkage. |92. .'Ihsey.'V are preferably keyed on theLsameshat asi the contactorsy |12, |.16 and |171... From; member |91 are drawn. the; local; oscillations: injected; by thel grids' I 82.and |,B3.into1 the frequencygchanging tubefxl 8| Grid. |83 .is a: part4 of a triodeandigrid` |82fis apartlof azhexode; Whose platesgland |9411 are; fitted 1 int opposition. and whose: common circuiti has: two.: windings. |85. and; |961. Both Windngshave effects: of equal .but Vopposite; value onza secondary; winding-f l 957 dueto; thea selection oftlie; coupling'coefcients of; windings. |95 andi |96 .with Winding. |91. This .layout 1 avoids; lock:- ing: of .the followingf frequency: changing; tube. 98 under theacti'onof the firstlocal Voscillations'. Said. frequency` changing.n tube is fedon` its` grid 99 :by the vintermediate..oscillationsifronrtube; i 8l.

` and; orritszgridlZB" by the second localkv oscillations supplied. by; the. triodfefoscillatcr: 2.6 l.A insertedii in tube I98;.Whose*frequencymay. vary ina continiuous manner: under.:` the-` action. of; the.' oscillating; circuit: 202.-: comprising; aA variable capacitor 203'; 'Iherzvariablecapacitors- |173.;y Hilf and 2ll3. areLcoupled .by a linkage 20.4; They. areA forfex'.- axnulevfitted and` keyedto; at. saineA shaft.. The resulting' oscillations.. fromi. tube |98', having passed. theiplata circuit 2.04; Will constitute? the intermediate.; frequency-oscillations; ofi theireceivr er; whichare. treatedingtheiusual mannen The:inventionhereinbefore; describedwith' .ref ernc to specific examples is.; obviously not limited tor'the features givenzby'way-of illustration: but includes'. all4 variations. or: modifications.: thereofl fallingiwithirrthei spirtor: scope of `theappended claims:

It'willgbe; understood,.that; if: desired, azsecond crystal controlled" oscillator: may" have; itsgoutput mixed/with` continuously'variabletoscillationsand the sum. or-differenca applied to;- mixer. tubef |98; as-foutlinedzin the, foregoinggdiscussion relative to. Fi'guresfZ; 3:and;4.. 1

Whatisiclaimedisz.

1'.In a: system for; receiving radio=frequency signals: of any. frequency selected from a1 Wide; continuous. frequency band;.. iny combination: a radio; frequency circuit. for.' receiving4 said signal; a tunable: filter irr said radiofrequency circuit; said filter' beingtunable'- over all: of jt-he said Wide frequency. band; a; firstt crystali stabilized; local oscillation generator`- supplying; a: discontinuous multiplicity ofuniformly spaced frequencies hav.- ingsa-.range'tlie limits .of which; substantially coincidewith1the-lmits of :said Wide frequencyband infthefrequency spectrum; a .first tuning element connectedztcisaidrst oscillation generatorforse leeting" one frequency from said discontinuous multiplicity; a: first-mixenconnected'A to the out.- putsi of both said. radio frequency' circuit and said first zstabilized local oscillaticngeneraton, a second tunable ltenconnectedt'o theV cutout of said mixerA and tunable over an'interval' substantially. narrower than saidI Wide frequency band, saidnterval beingv substantially not greater than the'interval between any.twosuccessivefree 114i quencies.y of. the uniformly. spaced: first: looalpjos': cill'ationsf. and. positionedn'l the.. frequency:speerl trum toward.; the;y lower.` limit: of said; Widez free' quency. band; a.second;local.oscillationigeneraton variable over.' substantially'fthe.;samegintervalxboth inv Width. and: frequency" as.. said", seconda lt'er.; a.. second? tuning element?v connected; to; said sec;-

ondi. locali oscillationgenerator'for: varying; the.v

frequency 'of said secondilocaloscillation; gener;- ator, a.second..mixer. connected. toathezoutputs ofi both. said. second filter. andl {saidsecond. local oscillationgenerator, f ai third filter; connectedf; to. the' output.V of said secondzmixer; andi tuned to' a fixed. intermediate;y frequency. said filter: hay;

ingaband passwhose Width issubstantially less.`

than any; @f1-the; previous; frequencies; a, single control; connected. to both'.` said; first tuning: ele'.- ment and.' to saidrsttunable; filter: for simultaneously` selecting. one. ofi saidt multiplicity of..

uniformly spaced". frequencies; and'. adjusting :the pass frequenciestof 'saidifilter anda. second.r singley controli connectedn tof both. said second .tuning element; and both of.: said: first and.Il second tun.- able filters forsimultaneouslyadjusting the; fre.'- quencies. of. saidrlilt'ersV andfsaid second; locales-v cillationigenerator; l

2.; In a system; for; receiving; radio: frequency signals'. of. any frequency.- selectedpfromy a wide; continuous frequency band. inu combinations: a radio1frequencycrcuit; for receivingv said signal, a. rst; tunable. filter: connectedginto; said radio frequency'- circuit;v said filter being. tunable; over' all.. of said wide: band; aA crystalstabilized local oscillation generator, a harmonics generator con;V

nected'tothe output-of saidzlocaloscillation.gen-

eratorandzsupplyingza discontlnuousgmultiplicity of uniformly spaced frequencies;r havingA arrange the. limits. of which.substantially,l coincide .with they limits of.V saidrwide; frequency; band: in'. the frequency spectrum; a; first' mixer; connected-'.to the .outputs of'liotlr saidharmonicsizgeneratorfand said? radio; frequency circuit;V an. secondi tunablev filter.' connected .to the'v output of saidirstmixer andi. tunable'v over; an; interval substantiallyfnar rowenthan; said Wide vfrequency-band; saidi.in,ter. valbeing-substantially vnot-greatentharntheintere vallbetvveen4 anyftwo successiveifrequencies-offthe harmonics generator. and postionedzinftheffref quency;y spectrumitoward; the-lower, limits; of; said Wide; frequency band; a second; locali oscillation generator variabler over.: substantially the; same frequency` interval as; said?. second; filter;n a. second mixer: connectedto: the: outputs? of; bot-h. said scondfilter:and-.saidsecondzlocal:oscillationgcnf erator. ai first single; control 'connected toi both saidA harmonics` generator and said-first; tunable filter for,l simultaneously..` selecting-one.l ofl said multiplicity; ofzuniformlyspacedfrequenciesfand foradjusting the' pass frequency'of: said| filter; and an secondi single,A controlA connected tofI bot-h said secondrloca'l: oscillation generator.` andisaid i'rstA and .second ftunable filters for simultaneous:- ly: adjusting: the; frequencies of. said-.f oscillation generator and-said filters; anclfav thirdffilter A connecteqto: the output of saidgsecondf mixergand tuned to fixedintermediate frequency.

3;.In` a-systemi for; receivingy radio. frequency signals of anyV frequency selected'. fromza Wide, continuous: frequency band, in combinationfza radio2 frequency circuit forfreceivingsaidesignal; a; first'. tunable` filter connected into;- said? radio frequency circuit, i said filtery being., tunable over all .of said.'` Widei band; ai. crystal stabilizedx local oscillation generator; a harmonics Pgenerator;con-f necteckto: the output; of saidoscillation generator and. supplying` a discontinuous multiplicity of uniformly spaced frequencies having a range the limits of which substantially coincide with the limits of said wide frequency bandA in the frequency spectrum, a first mixer connected to the outputs of both said harmonics generator and said radio frequency circuits, a second tunable filter connected to the output of said first mixer and `tunableA over an interval substantially narrower than said wide frequency band, said interval being substantially not greater than the interval between any two successive frequencies of the harmonics generator and positioned in the frequency spectrum toward the lower limit of said wide frequency band, a second local oscillation generator variable over substantially the same frequency interval as said second filter, a second mixer connected to the outputs of both said second filter and said second local oscillation generator, a first single control connected to both said harmonics generator and said first tunable filter for simultaneously selecting one of said multiplicity of uniformly spaced frequencies and for adjusting the pass frequency of said filter, a second single control connected to both said second local oscillation generator and said first and second tunable filters for simultaneously adjusting the frequencies of said oscillation generator and said filters, a third filter connected to the output of said second mixer and tuned to a fixed intermediate frequency, and means connected to the output of said third filter for detecting and amplifying the said output.

4. In a system for receiving radio frequency signals ofany frequency selected from a wide, continuous frequency band, in combination: a radio frequency circuit for receiving said signal, a first tunable filter in said radio frequency circuit, said filter being tunable over said wide frequency band, a first crystal stabilized local oscillation generator for supplying a discontinuous multiplicity of uniformly spaced frequencies having a range the limits of which substantially coincide with the limits of said Wide frequency band in the frequency spectrum, a first mixer connected to the outputs of both said radio frequency circuit and of said first local oscillation generator, a second tunable filter connected to the output of said first mixer and tunable over an interval substantially narrower than said wide frequency band, said interval being substantially not greater than the interval between any two successive frequencies of said first local oscillation generator and positioned in the frequency spectrum towards the lower limit of said'wide frequency band, a second crystal stabilized local oscillation generator supplying a second discontinuous multiplicity of uniformlyl spaced frequencies having a range the limits of which are substantially equal to the interval between any two successive frequencies of said first local oscillation generator, a third local oscillation generator continuously variable over a range the limits of which are substantially equal to the interval between any two successive frequencies of said second local oscillation generator, a second mixer connected to the outputs of both said second and said third local oscillation generators, a third tunable filter connected to the output of said second mixer, a third mixer connected to the outputs of said second and third tunable filters, a first single control 'connected to said first local oscillation generator and to said first tunable filter for simultaneously selecting one of said multiplicity of uniformly spaced frequencies and adjusting the pass frequencies of said filter, a second single control connected to said first, second, and third tunable filters and to said second local oscillation generator for simultaneously selecting one of said second multiplicity of uniformly spaced frequencies and for adjusting the pass frequencies of each of said filters, and a third single control connected to said second and third tunable filters and to said third local oscillation generator for simultaneously adjusting the frequencies of both of said filters and said thir local oscillation generator.

5. In a system for receiving radio frequency signals of any frequency selected from a wide, continuous frequency band, in combination: a radio frequency circuit for receiving said signal, a first tunable filter connected into said radio frequency circuit, said filter being tunable over said wide frequency band, a first crystal stabilized local oscillation generator, a first harmonics generator connected to the output of said first local oscillation generator and supplying a discontinuous multiplicity of uniformly spaced frequencies having a range the limits of which substantially coincide with the limits of said wide frequency band in the frequency spectrum, 'a first mixer connected to the outputs of both said radio frequency circuit and said first harmonics generator, a second tunable filter connected to the output of said first mixer and tunable over an interval substantially narrower than said wide frequency band. said interval being substantially not greater than the interval between any two successive frequencies of said first harmonics generator and positioned in the frequency spectrum towards the lower limit of said wide frequency band, a second crystal stabilized local oscillation generator, a second harmonics generator connected to the output of said second local oscillation generator and supplying a second discontinuous multiplicity of uniformly spaced frequencies having a range the band width of which is substantally equal to the interval between any two successive frequencies of said first harmonics generator, a third local oscillation generator continuously variable over a range the band width of which is substantially equal to the interval between any two successive frequencies of said second harmonics generator, a second mixer connected to the outputs of said second harmonics generator and said third local oscillation generator, a third tunable filter connected 'to the output of said second mixer,Y a third mixer co'nnected to the outputs of said second and Vthird tunable filters, a first single control connected to said first harmonics generator and to said first tunable filter for simultaneously selecting one of said first multiplicity of uniformly spaced frequencies and for adjusting the pass frequencies of said filter, a second single control connected to said first, second and third tunable filters and to said second harmonics generator for simultaneously selecting one of said multiplicity of uniformly spaced frequencies and for adjusting the pass frequencies of each of said filters, and a third single control connected to said'second and third tunable filters and to said third local oscillation generator for simultaneously adjusting the frequencies of said filters and of said local oscillation generator.

6. In a systemv for receiving radio frequency signals of any frequency selected from a wide, continuous frequency band, in combination: a radio frequency circuit for receiving said signal,

i quencies having a range the limits of which substantially coincide with the `limits offsaidwide frequency band in the frequency spectrum, a

rst mixer connected to the outputs of 4both-said radio frequency circuit and said first harmonics generator, a second tunable'filter connectedfto the output Yof said first mixer and tunable over an interval substantially narrower than said wide Vfrequency band, said interval being substantially not greater than the interval between any two successive frequencies of s'aid'first harmonics generator land positioned in the frequency spectrum towards the lower limit lof saidwide `frequency band, a second crystal stabilized vlocall oscillation generator, a second harmonics generator connected to the output of said second local oscillation generator and supplying a second discontinuous multiplicity of uniformly spaced frequencies having a range the band width of which is substantially equal to the interval between any two successive frequencies of said first harmonics generator, a third local oscillation generator continuously variable over a range the band width of which is substantially equal to the interval between any two successive frequencies of said second harmonics generator, a second mixer connected to the outputs of said second harmonics generator and said third local oscillation generator, a third tunable filter connected .to the output of said second mixer, a third mixer connected to the outputs of said second and third tunable lters, a rst single control connected to said rst harmonics generator and to said first tunable filter for simultaneously selecting one of said first multiplicity of uniformly spaced frequencies and for adjusting the pass frequencies of said filter, a second single control connected to said first, second and third tunable filters and to said second harmonics generator for simultaneously selecting one o f said multiplicity of uniformly spaced frequencies and for adjusting the pass frequencies of each of said filters, a third single control connected to said second and third tunable filters and to said third local oscillation generator for simultaneously adjusting the frequencies of said filters and of said local oscillation generator, and amplifying A and detecting means connected to the output of said third mixer.

7. In a system for receiving radio frequency signals of any frequency selected from a wide, continuous frequency band, in combination: a tuned means to which radio frequency signals are applied, a crystal stabilized local oscillation generator supplying a discontinuous multiplicity of uniformly spaced frequencies having a range substantially coinciding with said wide frequency band in the frequency spectrum, a first tuning element connected to said first local oscillation generator for selecting one frequency from said discontinuous multiplicity of frequencies, a first mixer connected to the outputs of both said first local oscillation generator and said antenna, a second local oscillation generator continuously variable over an interval substantially narrower than said wide band, said interval being substantially not greater than the interval between any two successive frequencies of the uniformly spaced first local' oscillations fqiiencyspectrumtoward the lower limit of said f wide frequency band, a second tuning element connected to said second'local oscillation generator anda second'mixer connected to the outputs and lpositioned in the freof both -said second local oscillation generator and `saidv first mixer, wherein said first stabilized lzal oscillation generator comprises a crystal -stabilized oscillator, an electronic tube having a first grid fconnected'to the output of said oscillator'and a vplate circuit including a first os- ,cillatorycircuit, a harmonics generator coupled with: said'oscillatory circuit, and a second oscillatory vcircuit coupled with said harmonics generator'fand connected'to a second grid of said tube, whereby said tube may operate as a frequency changer; v

8. In asyster'n for receiving radio frequency signals of any'frequency selected from a wide, continuous'frequency band, in combination: a tuned means' towhich radio frequency signals are applied, a crystal stabilized local oscillation generator supplying a discontinuous multiplicity of uniformly spaced frequencies having a range substantially coinciding with said wide frequency band in the frequency spectrum, a first tuning element connected to said first local oscillation generator for selecting one frequency from said discontinuous multiplicity of frequencies, a first mixer connected to the outputs of both said first local oscillation generator and said antenna, a second local oscillation generator continuously variable over an linterval substantially narrower than said wide. band, said interval being substantially not greater than the interval between any two successive frequencies of the uniformly spaced first local oscillations and positioned in the frequency spectrum toward the lower limit of said wide frequency band, a second tuning element connected to said second local oscillation generator and a second mixer connected to the outputs of both said second local oscillation generator and said first mixer, wherein said first stabilized local oscillation generator comprises an oscillator, two crystals controlling the frequency thereof, a selector for selectively connecting either one of said crystals to said oscillator, an electron tube having a first grid coupled with said oscillator and a plate circuit includinga first oscillatory circuit, a harmonics generator coupled with said oscillatory circuit, and a second oscillatory circuit coupled with said harmonics generator and leading to a second grid of 'said tube, whereby said tube may operate as a frequency changer.

9. In a system for receiving radio frequency signals of any frequency selected from a wide, continuous frequency band, in combination: a tuned means to which radio frequency signals are applied, a crystal stabilized local oscillation generator supplying a discontinuous multiplicity of uniformly spaced frequencies having a range substantially coinciding with said wide frequency band in the frequency spectrum, a first tuning element connected to said first local oscillation generator for selecting one frequency from said discontinuous multiplicity of frequencies, a first mixer connected to the outputs of both said first local oscillation generator and said antenna, a second local oscillation generator continuously variable over an interval substantially narrower than said wide band, said interval being substantially not greater than the interval between any two successive frequencies of the uniformly spaced first local oscillations and positioned in 19 the kfrequency spectrum toward the lower limit of said wide Vfrequency band, a secondtuning element connected to said second local oscillation generator and a secondA I nixer" connected to the outputs of both said second local oscillation generator and saidfirst mixer, wherein said stabilized local oscillation generator comprises an oscillator, 1 two crystals controlling the frequency thereof, a selector for selectively connecting either Ao ne of said crystals to said oscillator, an electron tube having a rst grid coupled with said oscillator and a plate circuit including a first oscillatory circuit, a harmonics generator coupled with said oscillatory circuit, and a second oscillatory circuit coupled with said harmonics generator and leading to the second grid of said tube,

20 REFERENCES CITED The'ollowing references are of record in the Number Name Date 2,017,712 Downey Oct. 15,v 1935 2,055,737 Terman Sept. 29, 1936 2,131,558 Granger Sept. 27, 1938 2,150,553 Koch Mar. 14, 1939 2,150,562 Reid Mar. 14, 1939 2,173,898 Copron Sept. 26, 1939 2,186,980 Lowell Jan. 16, 1940 2,209,959 Chittick Aug. 6, 1940 2,215,775 Baneld Sept, 24, 1940 2,263,634 Landon Nov. 25, 1941 2,265,083 Peterson Dec. 2, 1941 2,270,023 Ramsey Jan. 13. 1942 2,282,092 Roberts May 2, 1942 A2,354,14f8 ShawV July 18, 1944 2,360,764 Crosby Oct. 17, 1944 

